Photic regulation of arylalkylamine N-acetyltransferase I mRNA in trout retina

Melatonin production in the pineal organ and retina is controlled by both l ight-dark cycles and a circadian clock via the oscillating activity of aryl alkylamine N-acetyltransferase (AANAT) in most vertebrates. However, this c lock regulation is absent in the rainbow trout (Oncorhynchus mykiss) pineal organ: the trout has two different AANAT genes (AANAT1 and AANAT2), and AA NAT2 mRNA levels in the pineal organ did not exhibit circadian oscillation In this study, we confirmed by RT-PCR analysis that AANAT1 is expressed onl y in the retina, while AANAT2 is expressed in the pineal organ and brain. R eal-time quantitative PCR analysis demonstrated that AANAT1 mRNA levels in the retina exhibited daily variations with high levels during the dark phas e under light-dark cycles, but kept high and low titers under constant dark ness and constant light, respectively. Thus, AANAT1 gene expression in the trout retina is regulated not by a circadian clock but by lighting conditio ns. NeuroReport 11:3473-3477 (C) 2000 Lippincott Williams & Wilkins.